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Midterm 1 Flashcards

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1
Q

What does the cytoskeleton do?

A

● supports cell shape, cell movement, and internal rearrangement of cellular structure
● important for transport and cell cycle (chromosome segregation)

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2
Q

What specifically supports chromosome segregation?

A

●microtubules
● (in the DNA)

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3
Q

What parts of the cytoskeleton drive cytokinesis?

A

●microtubules
●actin (concentration of actin)

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4
Q

What are the components of cytoskeleton?

A

●Three filament systems: actin, microtubules, intermediate filaments

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5
Q

What bonds are used within the filaments?

A

●noncovalent bonds

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6
Q

Actin

A

●is a polymer
●made of actin monomers
●support cell membrane and shape
●contractive structure with myosin

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7
Q

Microtubules

A

●polymer
●monomer is tubulin
●less strong than actin
●thicker
●form network within cell
●movement of vesicle around cell
●important for shape and cell division (pull chromosomes apart)
●cylinder shape

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8
Q

intermediate filaments

A

●in skin cells
●connect cell together

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9
Q

What can cytoskeleton impose?

A

●polarity
●remodel themselves

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10
Q

Actin subunits

A

●form F-filaments
●not symmetrical (plus end and minus end)
●can polymerize and depolymerize
●contain energy (ATP)

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11
Q

Actin Polymerization

A

●form without proteins or protein mediated
●50% of actin in filament, 50% as monomer
●nucleation: actin subunits until forming actin nucleus (three)
●elongation: exponential growth after nucleus is formed until equilibrium is reached
●steady state: equilibrium, treadmilling

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12
Q

Forming actin filament

A

●Free actin monomer (T-form) associated with ATP
●ATP hydrolyzed to ADP when subunit associates with filament (G-form)
●monomers associated with ADP are more likely to dissociate from filament (less stable bond) (slow dissociation)

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13
Q

Actin in steady state

A

●length remain constant
●plus and minus end
●treadmilling
●filament moving forward
●rate of addition of one subunit= rate of removal of one subunit
●polymerization=depolymerization

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14
Q

Proteins mediating nucleation of Actin

A

●Arp2, Arp3 Complex (active when associated with NPF)
●facilitate nucleation of actin monomers
●located at minus end (stabilize and avoid depolymerization) (cap like)
●essential for branching (important for complex structures)
●cell cortex (small layer of proteins under membrane)

●Formins complex (dimer, circle like structure)
●bond to plus end of filament
●facilitates nucleation

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15
Q

Elongation regulation

A

●by monomer-binding proteins
●Profilin binds to actin monomer
●opposite side of the ATP binding site
●Profilin favors addition of monomer to plus side

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16
Q

What are the three movements?

A

●mesenchymal cell migration
●ameboid and bleebing cell migration

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17
Q

Contractive structures actin

A

●two filaments of actin slide relative to one another
●sliding is driven by myosin
●cell migration and muscular contraction
●head of myosin hydrolyzes ATP (N-terminal)
●has coiled-coil tail (C-terminal)

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18
Q

Myosin in skeletal muscles

A

●form thick filaments
●multiple myosin heads oriented in opposite directions
●essential for muscle contraction

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19
Q

Myosin slides actin filaments

A

●myosin heads attached to actin filament (looking at myosin II)
●myosin head detaches from actin filament when ATP binds (conformational change)
●ATP causes conformational change where myosin head is displaced along filament. Then ATP is hydrolyzed (change of position is very small, flip head a little bit)
●myosin head binds to new site on actin filament
●ADP and phosphate are released (another conformational change after release that creates force to slide filament)
● myosin head in rigor position again, ready for new ATP

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20
Q

Skeletal muscle cells

A

●made of lots of sarcomeres (small circular unit)
●dark band (myosin) and light band (actin)
●z disc is dark line that separates sarcomeres
●when relaxed thick and thin filament are spread out
●when contracted thick and thin filaments are overlapping almost entirely

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21
Q

Mechanism of contraction

A

●tropomyosin: filament protein that binds along grooves of actin filament (long line)
●troponin complex: protein that binds Ca2+, actin filament, inhibitory function (small bundle of proteins)
●When Ca2+ binds to troponin complex the tropomyosin filaments change conformation opening sites for myosin heads to interact (troponin and tropomyosin are connected)

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22
Q

Microtubule in detail

A

●form as dimer between alpha-tubulin and beta-tubulin
●hollow structure
●GTP used as energy (only on one monomer, the beta-tubulin)
●protofilament is long line of dimers (linear row)
●highly dynamic
●GTP hydrolysis weakens affinity by changing conformation (depolymerization)
●plus and minus end

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23
Q

Dynamic Instaibility

A

●rapid growth with GTP-capped end (with more growth GTP slowly lost)
●random loss of GTP - cap (because dimers near + have GTP)
●rapid shrinkage (catastrophe)
●regain of GTP cap (rescue)
●rapid growth with GTP-capped end
●found when chromosomes are pulled apart
●REMEMBER EVERYTHING IS HIGHLY REGULATED

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24
Q

What does the cell membrane do?

A

defines cell boundaries

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25
What is the cell membrane made of?
●lipids and proteins
26
What are some properties of the cell membrane?
●Phospholipid bilayer ●Glycerol phospholipids (cause asymmetry) ●Self-assembly ●fluid ●semi-impermeable ●other lipids: sphingolipids, glycolipids, and steroids (cholesterol)
27
Phospholipids
●glycerophospholipids (GLPs) are most abundant in cell ●amphiphilic ●composition of GLPs can vary ●head is polar, charged (contains glycerol, phosphate, and head) ●hydrocarbon tail that is non polar (fatty acid) ●kink is caused by unsaturated fatty acid (double bond)
28
Sphingosine
●contains sphingosine instead of glycerol ●amphiphilic
29
Cholesterol
●steroid ●amphiphilic ●rings ●shorter hydrocarbon chain ●more rigid
30
Glycolipids
●sugar-containing lipids ●asymmetric (different properties) ●sugar always facing the extracellular environment ●protection, cell adhesion, cell-cell interaction ●immune system recognition
31
Why is the hydrocarbon chain hydrophobic?
●because it can not H-bond with the H2O in the environment
32
Lipids packaging in water
●one tail: create micelle (sphere) ●two tails: phospholipid creates bilayer, energetically favorable
33
Formation of closed compartment
●free edges of bilayer are exposed to water and it's not energetically favorable ●lipid bilayer rearranges itself to eliminate the edges ●bilayer closes into compartment that is favorable
34
Cell membrane is fluid
●lipids and some protein diffuse freely in membrane and across bilayer (less frequent)
35
Flip-flop
●not frequent ●important ●inner to outer layer
36
Flexion
●has kink
37
Rotation
●rotation of lipid on itself ●phase transition
38
Factors affecting membrane fluidity
●temperature: phase transitions, short hydrocarbons tails lower crystallization point, higher temp breaks double bonds (more fluid at higher temps), van deer waals bond between phospholipids ●unsaturated fatty acids: kinks in lipid tails makes them more difficult to pack together (more unsaturated= more fluid) ●cholesterol: stiffen lipids (more cholesterol= less fluidity)
39
Asymmetry of cell membrane
●in lipid composition and protein structure ●critical physiological role ●inner membrane property diff than outer ●highly regulated (synthesis and location)
40
Membrane proteins
●integral proteins: transmembrane and membrane-associated (embedded into cell membrane), lipid-anchored ●peripheral proteins: interact with cell membrane through noncovalent interactions (protein-lipids) ●proteins are amphiphilic ●protein-membrane association reflect protein function in cell
41
Transmembrane proteins
●single or multipass transmembrane protein
42
Lipid metabolism
●lipidic composition of cell membrane (every membrane) is essential for structure and function ●MEMBRANE HOMEOSTASIS (stable internal environment- equilibrium) (process unknown) ●lipid-related diseases
43
Membrane transport
●permeable to impermeable ●selective permeable ●depends on dimension and charge ●nonpolar, small molecules -> polar, uncharged small molecules -> polar, uncharged large molecules -> small ions (charged, polar)
44
Examples of nonpolar, small molecules
●O2, N2, CO2
45
Examples of polar, uncharged small molecules
●H2O, glycerol
46
Examples of polar, uncharged large molecules
●glucose, sucrose
47
Examples of small ions
●K+, Na+
48
Velocity of membrane transport
●permeability coefficient: how fast a molecule cross a membrane ●artificial membrane: lipidic membrane without proteins made in lab (only phospholipid bilayer - no proteins)
49
Simple Diffusion
●small nonpolar molecules diffuse very rapidly ●O2, N2, CO2 ●No need of transporters or channels ●regular diffusion
50
transporters
●some require energy ●transmembrane ●called also carriers or permeases ●bind to specific solute ●transporters undergo a conformational change to expose solute binding site on one side of membrane
51
Channels
●transient interaction with solute ●extend across membrane ●transport with channels is faster than with transporters
52
What are the membrane transport proteins?
●transporters and channels
53
Protein Structure of Transporter
●PDB code 3F3E ●Na+/Leu symporter in bacteria ●homologous in human ●multi-pass transmembrane protein (same thing in reverse) ●openings at the opposite sides of cell membrane are the same
54
Passive Transport
●channels and some transporters ●uncharged molecules diffuse towards less concentrated environment (concentration gradient, downhill) ●transport of charged molecules depends on concentration gradient and membrane potential of membrane (electrical properties- established by currents of ions) ●no energy ●concentration gradient + membrane potential= electrochemical gradient
55
Passive Transport and Membrane Potential
●ionic currents between the cytoplasm and extracellular environment establish the membrane potential (volt) ●membrane potential usually neg inside (more K+ leakage than Na+ influx) ●membrane potential can change due to ionic currents ●transport of polar molecules (ions) is affected (electrochemical gradient)
56
Kinetics of cell membrane transport
●rate of rxn (how fast things go) ●diffusion or channel-mediated transport is linear ●carrier-mediated transport goes from linear to plateau (all carriers get occupied) (1/2 Vmax and V max) (Km constant)
57
Active Transport
●against electrochemical gradient (uphill) ●need energy ●transporters are coupled with source of energy to pump against concentration ●evolutionary conserved
58
Coupled-transporters
●transport of one solute depends on the other solute transported ●symporters transfer solutes in same direction (one supports mvmt because it follows the concentration gradient) ●antiporters transfer solutes in opposite direction
59
ATP-driven pumps
●P-type pump: auto-phosphorylation, maintain ionic gradient, for H+ K+ Na+ Ca2+ ●ABC transporter (ATP binding cascade): pump small molecules (hydrolysis of ATPs)
60
Ca2+ pump or Ca2+ ATPase
●sarcoplasmic reticulum (SR) serves as storage of Ca2+ ●when membrane of SR depolarizes Ca2+ is released in cytoplasm via Ca2+ channels ●Ca2+ pumps and Ca2+ ATPase pump Ca2+ back in SR ●Skeletal muscles cell ●Nucleotide-binding domain, phosphorylation domain, actuator domain
61
Ca2+ pump or Ca2+ ATPase mechanisms
1. ATP on N domain, 2H+ out of pump, 2Ca2+ in (from cytosol) 2. conformational change of pump once Ca2+ has bound to binding site 3. ATP has hydrolyzed and phosphate attaches to p domain 4. ADP swapped for ATP 5. induce conformational change where Ca2+ is pushed out into the sarcoplasmic reticulum and 2H+ goes in 6. Phosphate group is released and causes another conformational change where the pump is returned to it's original state
62
Ion channels
●channels dedicated to transporting ions ●not coupled with energy (passive) ●ion selective ●selective filter (narrow part of channel) ●amino acids make filter ●ion channels are gated= open in response to stimulus (important for activity)
63
Extracellular stimulus that open ion channels
●Change in voltage (voltage-gate channels- membrane potential) ●mechanical stress (mechanical gated channels)(think pressure) ●binding of ligand (ligand-gated channels): transmitters, nucleotides, ions, phosphorylation and dephosphorylation (regulatory)
64
Types of gated-ions channels
●voltage-gated channel are present in neurons, muscles, some endocrine cells, and bacteria ●ligand-gated channels are found in neurons, cardiomyocyte ●mechanically-gated channels are found in animals and bacteria, skin cells ●always open, K+ is important to maintain membrane potential
65
Membrane potential: role of K+
●in animal cells ●all membranes have potential ●membrane potential in animal cells is mainly generated by passive ion transports through the channels ●resting membrane potential: no net flux of ions across in and out the membrane ●membrane potentially largely depends on K+/Na+ pumps and K+ channels (K+ leak- always open) ●resting membrane potential is neg (-170mV and -70mV) (neurons) ●bacteria, fungi and plants also have membrane potential ●concentration always same ●nerst equation: calculates voltage gradient at equilibrium
66
Electrochemical gradient
●combination of concentration gradient and voltage gradient
67
Membrane potential: role of Na+/K+ pump
●in animal cell ●Na+/K+ pump will pump 3 Na+ outside the cell and 2 K+ inside ●uses ATP ●Establishes concentration gradient for K+ (leaves behind neg charge as K+ moves to one part)
68
Bacterial K+ channel
●K+ channel highly selective for K+. Highly conserved. ●Mutation in residues interacting with K+ are lethal ●K+ channels can open or close. they can respond to membrane potential or ligand binding ●Na+ out= mess up membrane potential ●selectivity filter: see diff between ions, can't interact same way with Na+ ●uses carbonyl oxygen
69
Mechanosensitive channels: how cells sense their physical environment
●extracellular forces: stretching, compressing, shear force, gravity, sounds waves ●intracellular forces: pressure ●extracellular matrix, cell stretching
70
PIEZO1/2 channels
●converting mechanical forces into electrical signals ●PIEZO 1 and PIEZO 2 are ion channels (PIEZO 1: Ca2+ preferably Na+, K+, Mg2+) (PIEZO 2: non-selective) ●trimeric complex: 36 alfa helixes each ●homologous in C. elegans and drosophila ●in bacteria different mechanosensitive channels (MSCs) ●channels mediate mechanotransduction processes ●mutations in PIEZO proteins can lead to diseases and lethality
71
Mechanotransduction
●process by which mechanical forces are converted into biochemical signal (activate other proteins)
72
Mechanosensitive channels in bacteria MSCs
●two domains (1 transmembrane and 1 intermediate), seven transmembrane helices ●change conformation in response to cell membrane stretching ●cell membrane stretches in response to changes in osmotic concentration in extracellular environment ●opening channels reestablishes osmotic equilibrium ●hypertonic: water leaves and bacteria shrinks ●hypotonic: extracellular has higher solute concentration, increase pressure inside
73
Neuron message
●signals are transfer across the nervous system as electrical impulses ●latter travels along cell membrane ●impulse also called action potential ●signals transfer as electrical impulse
74
Values of membrane potential
●resting membrane potential at -70 mV ●depolarization (less neg) ●hyperpolarization (more neg)
75
1) action potential trigger by membrane depolarization
●membrane must depolarize to a certain extent to open gates ●membrane depolarization induces opening of voltage-gated Na+ ●one polypeptide chain, for domains. ●voltage sensor perceives changes in membrane voltage ●voltage sensors (sense of voltage of membrane) ●pore= filter
76
2) Na+ enter inside the cell depolarizing the cell membrane even further
●membrane depolarization induces opening of voltage-gated Na+ ●Na+ enters inside cell propagating stimulus and depolarizing membrane even further (positive feedback) ●More Na+, more channel open, more depolarization ●Na+ high on outside of cell, K+ high inside
77
3) Na+ channels inactivate, and voltage-gated K+ channels open
●Na+ channels automatically inactivate ●cell reaches another resting state where electrochemical gradient that drives Na+ is zero (too positive charge inside cell) ●depolarization stops because of electrochemical gradient -> lots + in cell -> less Na+ enter -> resting state, no gradient anymore for Na+ to enter ●no more influx of Na+ (INACTIVE- NOT CLOSED) ●after few msec, K+ voltage-gated channels open. K+ leaves cell. Rapid repolarization of membrane ●Na+ channels stay inactive until membrane potential is sufficiently negative ●period of inactivation called refractory period- important because it avoids repetitive firing and ensures the unidirectionality of stimulus ●in closed state- cell can always be depolarized ●recover is dip below resting potential where a new action potential can not be started
78
Na+ Voltage-gated channel mechanism
●Na+ exists in three states ●closed (+ on extracellular, - on cytosol) ●inactivated (charges flipped, membrane refractory) ●open (membrane depolarization ●with only open and close states- never have recovery
79
Myelin accelerates propagation of impulse
●axons are long ●nodes of ranvier, Na+ channels are concentrated so impulses "jump" from node to node and travel fast ●direction of impulse from dendrites to axon terminals
80
Light microscope (visible light)
●light source to illuminate system ●condenser is located below specimen and gathers light (shine only on sample) ●objective lens that magnify specimen (most expensive part) ●tube lens collect parallel lights from objective ●eyepiece
81
Electromagnetic spectrum
●visible light is small section 400nm to over 700nm

Adv Cell Bio (4 decks)

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